Photocatalytic conversion of CO2 using various TiO2 modified with Ag and Co dual cocatalysts via an ultrasonic reduction method

The photocatalytic conversion of carbon dioxide (CO 2 ) into high-value-added fuels and derivatives has attracted considerable attention as a technology for achieving carbon neutrality. To improve the activity for the photocatalytic conversion of CO 2 , it is important to modify the surface of semiconductor photocatalysts with suitable cocatalysts using an appropriate method. Although TiO 2 offers many advantages for practical use, it is considered unsuitable as a catalyst for the photocatalytic conversion of CO 2 to CO because its conduction band potential is close to the CO 2 /CO redox potential, resulting in a low driving force. In this study, Ag and/or Co cocatalysts were loaded onto various TiO 2 photocatalysts using several modification methods, including the ultrasonic reduction method (USR). TiO 2 showed the highest catalytic activity for the photocatalytic conversion of CO 2 with 2-propanol as a hole scavenger, when modified with Ag and Co dual cocatalysts by USR. Furthermore, a TiO 2 photocatalyst with a mixed anatase–rutile phase exhibited better photocatalytic activity than those with either anatase or rutile single phases, owing to more effective separation of the charge carriers. Consequently, a high CO formation rate with high selectivity toward CO was achieved using the AgCo/TiO 2 photocatalyst, in which the Ag and Co dual cocatalysts are loaded by USR onto TiO 2 with mixed anatase–rutile phases. This study demonstrated that cocatalyst composition optimization, loading method selection, and TiO₂ crystal phase choice can significantly enhance the efficiency and selectivity of the photocatalytic CO₂ conversion, offering a viable pathway for sustainable fuel production.